Sash balance



Feb. 3, 1953 D. TA PPAN SASH BALANCE Filed March 21, 1950 INVENTOR. DEWITT TAPPAN BY MM M HIS AGEN Patented F ch. 3, 1953 SASH BALANCE Bewitt Tappan, Irondequoit, N. Y., assignor to Ada 1'. Tappan, Irondequoit, N. Y.

Application March 21, 1950, Serial No. 150,871

11 Claims. 1

This invention relates to window sash balances, and it more particularly pertains to sash balances of the involute or clock spring type.

In balances of this type which are adapted to be mounted in the sides and at the top of awindow frame with the associated window sash supported therefrom by tapes, cables or the like, it is desirable to provide adjustable means for dampening the actuation of each balance so that a balance having a particular spring pressure can be adapted to balance its share of the weight of a window sash which is considerably lighter than the torsionalforce exerted by the balance as assembled. It is also desirable to dampen the operation of a balance slightly even if its torsional force can be accurately matched with the Weight of a window sash it is to balance so as to compensate for the difference in torsional force exerted by the balance, dependent upon the extent to which its spring is wound when the associated window sash is actuated to its respective extreme positions.

One method of obtaining the required dampening effect is disclosed in my prior Patent No. 2,241,969, dated May 13, 1941, but the dampening effect obtainable by this method has limitations which makes it diflicult to obtain sufiicient dampening without excessive strain and wear on certain of the parts of a balance, particularly when the balance is employed for handling relatively heavy window sash.

An object of the present invention is to apply dampening to a drum of a sash balance to a limited extent in a manner wherein the dampening efiect is applied substantially uniformly circumferentially about the axis of the drum of the balance by one means of dampening involving fixed biasing means set up upon the assembly of the balance.

Another obiect of the present invention is to provide additional dampening by reason of rotation of an adjustment disc about the axis of the drum of a sash balance, such additional dampening being effective to increase the dampening substantially evenly circumferentially about the axis of the drum.

Another object of the present invention is to provide means applying increased dampening at a plurality of different radial distances from the axis of the drum and thereby increase dampening by increasing the amount of friction surface as well as increasing the pressure between the friction surfaces.

Another obi'ect of the present invention is to render the dampening effect adjustable after installation of the sash balance, the adjustment being provided in a manner to promote rotation of the adjustment disc in either direction, in accordance with whether dampening is to be increased or decreased.

Another object of the present invention is to pl'wids an mpro ed a g for the drum of a sash balance which is particularly adapted to reduce the wear on a sash balance bearing to a minimum.

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawing and in part pointed out as the description progresses.

In describing the invention in detail, reference is made to the accompanying drawing, in which similar reference characters are used for designation of corresponding and similar parts and in which:

Fig, 1 is a plan view of the sash balance provided according to the present invention with a part of the cover broken away;

Fig. 2 is an elevational sectional view of the sash balance taken along the section line 2-2 of Fig. 1;

Fig. 3 is an end view of the sash balance shown in Fig. 1, illustrating the exposed portion of the balance when it is assembled within a window frame;

Fig. 4. is a sectional plan view of a portion of the balance illustrating the relative positions parts of the balance assume when adjustment is made to substantially a maximum dampening position;

Fig. 5 is a plan View showing the mounting of a bearing in the drum of a sash balance;

Fig. 6 is an elevational sectional view of a sash balance bearing mounting taken along the section line 6-6 of Fig. 5.

Fig. 7 is a sectional view of part of the dampening adjustment means taken along the section line l1 of Fig. 1; and,

- Fig. 8 is a sectional view illustrating the position of parts having to do with the adjustment of the dampening at a time when maximum dampening is obtained, taken along the section line 8-8 of Fig. 4.

The balance according to the present invention comprises a base plate l0, one end of which is semi-circular and of a diameter to conform to the outline of the balance. and the other end of the base plate Ill has a flange l l formed inward- 1y at rightuangles. The left-hand flange H (see Fig. 1) is adapted to receive an adjustment screw 12 as will hereinafter be considered. A face plate I 3 is suitably secured, as by welding, to the flanges ll.

Concentric with the semi-circular end of the base ID, one end of a hub I4 is secured to the base plate Ill so that it projects from the base plate It! so as to journal a drum IS. The hub M is tubular in shape with a longitudinal slot provided therein to serve as an anchorage for the inner end [6a of an involute spring IS. The hub [4 extends laterally entirely through the center of the balance and has ears I! formed in its left-hand end as viewed in Fig. 2, which when riveted over after assembly of a cover I8 on the balance, completes the balance assembly and maintains a bias spring pressure in a mamier and for purposes to be hereinafter considered.

A drum I has an end I9 journaled on the hub It as shown in Figs. 2 and 6. The end of the drum I5 is dished inward slightly for damp-v which normally remains stationary on the hub.

I6. Thus is provided: A radial bearing surface between the end I9 of the drum I5 and the hub I3, additional radial bearing surfaces between the inner concentric surfaces of the sectors 2I.

and the outer periphery of the ring 20, anda thrust bearing between the surface of the ring 26 and the drum end IS.-

The clock spring I6 when assembled within the drum I5 has its inner end IIiw-anchoredin a slot in the hub I4 as has been described, and its. outer end I61) is hooked over a detent 23 whichis formed inwardly from the periphery of the drum I5 as is illustrated in Fig. 1.

A window suspension tape 24 is secured to the outer periphery of the drum I5 and wound thereon by the torsional forceof the spring I6 to an extent limited by the tapeanchor loop 25, which is secured to the tape for facilitating the attach-.

ment to a window sash. Prior to the attachment ofa window sash, this tape loop servesas a stop 4 of the circle, although it is to be understood that thecamsmay takedifferent forms in accordance with the requirements of practice.

A cam pressure adjustment plate 3| is provided in the form of a disc having holes 32 and 32a formed therein for the respective cams and 30a of the base II] so that these holes 32 and 32a can be brought into direct registration with the cams 30 and 33a as is illustrated in Figs. 1 and 2 when the adjustment disc 3I is assembled over the hub I4 and brought into position adjacent the inner surface of the base I0. Disposed in the balance between the adjustment disc 3I and the dished end I9 of the drum I5 is a friction disc 33 of a suitable friction materialsuch as fiber. This. disc 33, they adjustment disc 3I and the base plate IiJ are all formed in a flat plane asconipared to the end I9 of the drum I5 being dished inwardly, as has been described and as is illustrated in Fig. 2.

In the assembly of the balance, the adjustment disc SI, the fiber disc 33, the. drum I5, and the 1 bearing ring 20 are respectively journaled on the'hub It, and a spacer washer 34 bearing, upon when it is drawn bythe tape up against a narrow slot formed in the flange I I and the face plate v26 as illustrated in Fig. 1. Th face plate 26. is formedslightly larger than the. flange II of the base plate so asito cover the edgesuof an-opening cut in the jamb of a window'frame formountingthe balance.

The hole 21 in the portion of the face plate26.

extending to the 'left'of the balance-assemblyzis provided for a mountingjscrewrsecuring' thebalance within a suitablesopening;f0rmed in-the jamb of a window-:f-rame; uponi its-installation into operating position. The hole .28-'(see Fig. 4)

in the face plate is provided opposite. the adjustment screw I2 and of a smaller-diameter: than the flat head of the adjustment screw so as to retain the adjustment screw I2 against longitudinal movement'in either directionas the.head29 of the screw I2 is lockedlbetween'san offset portion 35 of the'flange: II of the baseplate'ifl and the inner face of the face plate I3. :Th'e-hole 29' in the face plate I3 is provided'in registration with a cooperating hole (not shown) 'inthe periphery of the drum I5 so..that the insertion of a pin. throughthe; cooperating openings at the time. of attachment: ofrthe. tape" loop- 25* to a window. sash can relieve the tape 24 temporarily from the base: plate II) at a smaller radius and at circumferential positions. substantially I mid-- way between theiseries of ca-ms "provided at "the larger'radius. Thesecams are preferably circular :in shape 'as is illustrated inthe drawings with-the cam surfaces sloping toward'the center the innerturnsofthe spring I6 is disposed over the end of the hub I4 prior tothe. assembly of the cover .18 by reason of :the passage-of the. lugs I! of the hub- I ithrough. registrationopenings in the cover It. To assemble the cover I8.over the balance in this manner. it. is necessaryto apply pressure urging the coverover the lugs Has the lateral dimension of the spring. I6. the drum.-l5,,

and the. thickness of the. respectivefiben and adjustment discs is suchas: to. setupa biasing. pressure on the dished surface I9 ofItheudrumI5...

againstthe friction disc 33.when..the.cover I8,is retained in its assembled position by reason of the lugs I! being riveted. over after passage through holes in the cover.

It will thus be seen upon the assembly of the balance,:-pressure is applied by the cover I8 throughthe spacer 34,.the :inner turns of the spring I6, and .the.bearing.;rin 2!].against the dished end I9 of.the drum I5 so as to urge the drum i5 -to-bear againsttheflfiber disc 33 at a circumferential point of contact of a radius substantially comparable to the radius ofthe drum I5. This is because-the fiber disc. 33 and its associated adjustment plate areflatas compared to the inwardly dished end I9 of the drum I5, thus providing a space as illustrated in Fig. 2 between the fiber disc 33 and the-end I9 of the drum: I5,whenzthesashbalance is assembled with the holes 32'and 32a of the adjustment plate 3| in registration withthe cams 313 and 38a respectively formed from. the base IO.

Thusin this mannera minimum dampening is eiiectiverwith the holes :32 in :registration with the cams 36, such dampening being substan-,

tially -sufficient to prevent the automatic operationofa window because of junbalancing within the torsional :range of a spring I6 when actuated between its. extremepositions upon operation of an'associated'window sash'between its fully closed and. fully opened positions;

The actuation of the adjustment discZiI about the hub 'Id' afterrthe' balance is assembled accomplished byrotation of the adjustment screw 22.: This, screw I2 is disposed laterally spaced from the left-hand; inside. edge of the cover I3 (see Fig.1) 'byinsertionithrough' a hole inran inwardly formedoffset scrcw'head socket 35 of the flange II, and a hole in.a bracket 36 which is suitably attached tothebasei Iii.

The" lateral spacing .of :the :adjustment screw 2 from the inner side of the cover I8 is governed by the width of an adjustment nut 31 which is threaded onto the screw l2 and is locked against rotation by reason of the proximity of one of its flat sides to the inside surface of the cover I8.

Thus the adjustment nut 3! can be made to travel longitudinally along the screw |2 in one direction or the other in accordance with the direction in which the screw I2 is rotated upon the insertion of a screw driver blade through the opening 28 in the face plate I3. This operation can obviously be performed after the balance is assembled within the jamb of a window frame, and after a window sash has been attached to the tape 24 by means of engagement of the loop 25 with a suitable hook (not shown) attached to the edge of a window sash.

As the adjustment nut 31 travels longitudinally along the adjustment screw l2, it actuates the adjustment disc 3| about the hub M in one direction or another because of the engagement of the nut 31 within a suitable slot 38 (see Figs. 1 and 4) of an extending arm 39 formed integral with the adjustment disc 3|.

The slot 38 is preferably formed with crowned edges hearing at substantially opposite points against opposite sides of the adjustment nut 31 so that there is no free play for movement of the adjustment disc relative to the longitudinal movement of the adjustment nut 31. By the bearing surfaces being crowned substantially as illustrated in Figs. 1 and 4, the adjustment disc 3| can be freely operated between its minimum and maximum adjusted positions as shown in Figs. 1 and 4 respectively, with no free play provided at any point between these limits for the adjustment disc 3| relative to the longitudinal movement of the adjustment nut 37 along the adjustment screw l2.

To consider the dampening effect upon the rotation of the drum l5 by the spring I6 when the adjustment disc 3| is actuated, it will be assumed that increased dampening is found to be required for a balance assembled with the adjustment disc 3| in the position illustrated in Fig. 1 after the balance has been assembled within a window frame and operatively connected to a window sash.

To increase the dampening under these conditions, the screw I2 is rotated clockwise and the adjustment nut 31 is drawn axially along the adjustment screw |2 toward the face plate I3. The nut 31 thus carries with it the arm 39 of the adjustment disc 3| so as to rotate the adjustment disc 3| about the hub 14. Thus the trailing edges of the holes 32 for the direction of rotation are brought to ride upon the came 30 'of the base I0 so as to force the adjustment disc laterally to the left as viewed in Fig.2 away from the base plate l0, thus forcing the adjustment disc 3| to the left as viewed in Fig. 2 so as to hear more tightly against the friction disc 33 and thus urge this friction disc more tightly against the dished end IQ of the drum l5. With this added; pressure applied by the friction disc 33 against the end IQ of the drum I5, added dampening is obtained by added pressure being uniformly applied circumferentially to the drum Hi, the increase in dampening being proportional to the extent to which the trailing edges of the holes 30 ai e caused to ride up on the crowned cams 30 of the base |0 in accordance with the rotation of the adjustment screw l2 clockwise. Maximum dampening is obtained substantially where the relative positions of the cams 30 and the holes 32 are as illustrated in Fig. 4, wherein the trailing edges of the holes 32 have been brought to bear upon the highest portions of the respective cams 30, which are substantially the centers of these cams.

According to the nature of the balance as assembled, a biasing pressure is applied, as viewed in Fig. 2, through the inwardly dished end portion I9 of the drum l5, urging the drum 15 against the friction disc 33. It has been pointed out that this pressure is applied through the cover I8, the spacer 34, the inner turns of the spring I 6 and the bearing 20. Thus, an assembled, positive limitations against movement to the left as viewed in Fig. 2 for the end portion l9 of the drum 5 is provided at the point where the end portion I9 is journaled on the hub l4.

As the adjustment disc 3| is rotated counterclockwise as viewed in Fig. 1, this disc 3| is spaced farther from the base plate In as is illustrated in Fig. 8 by reason of the holes 32 being out of register with the cams 30, and thus circumferential pressure is applied to the end portion IQ of the drum l5, through the friction disc 33, causing movement of the periphery of the drum l5 to the left as viewed in Fig. 2. The center of the back portion |9 of the drum I5 is fixed at the point where the drum is journaled on the hub l4, however, with respect to the left-hand movement, as has been described, and thus the increase of pressure through the operation of the adjustment screw |2 tends to flatten out the dished portion I9 of the drum l5, which in turn provides that the end portion I9 of the drum l5 increases its contacting surface with the fiat friction disc 33, and thus increases the dampening uniformly circumferentially about the axis of the drum [5. That is, in this manner the dampening effect is produced not only by the increased pressure applied through the friction disc 33 to the end portion I9 of the drum l5, but is increased also by the increased braking surface created by reason of the dished portion of the end I!) of the drum l5 being flattened to conform more closely to the plane of the friction disc 33 and thus provide greater contact with that friction disc.

It is further provided that the inner circle of holes 3211 (see Figs. 1 and l) in the adjustment disc 3|, in cooperating with registration cams 30a of the base Ill, positively spaces the adjustment disc 3| the same distance from the base It as the earns 30 so that adequate dampening may be obtained with a minimum thickness of material for the adjustment disc 3|. That is, if the adjustment disc 3| were of relatively thin resilient material so as to maintain the ,over-all thickness of the balance at a minimum, without any inner circle of holes 32a and cooperating cams 30a, the pressure of the friction disc 33 against the end IQ of the drum 1% would be much more concentrated at the outer edge of the end portion I9, and thus in order to obtain the desirable degree of dampening, it would be necessary to concentrate so much pressure against a restricted area of the friction disc 33 that the disc 33 would wear rapidly and perhaps have to be replaced. It is therefore desirable that cooperating inner holes 32aand cams 30a be employed to positively insure that the friction surface is uniformly increased circumferentially about the axis of the drum -l5 as the adjustment disc 3| is rotated counter-clockwise as viewed in Fig. 1 by the driving of the nut 31 down- 7/ wardly axially; along the adjustment screw l2 by :therotation'of Ithe'adjustment screw I: in a clockwise direction.

It is to-be understood that if it is found in practice for a particular "range of window sash weights for which a balance is to be employed, that adequate dampening may be obtained by an increaserof'the friction surface alone without materially increasing-the pressure applied, the'outer circle of adjustment holes 32 may be eliminated, togetherwith their cooperating cams 38- of thebase l8, thus permitting adjustment to be made entirely by-the holes 32a cooperating with the cams 3011 which are rotated a substantially smaller-radius from the axis of the drum than the periphery ofthe drum l so that the action of the'adjustment disc 33 in cooperation with the camsSila under such conditions would merely tend to dish the adjustment disc 3! to conform to thecontour of the dished end E9 of the drum: l5.so as to increase the friction surfacebetween this end- [9 and the friction disc 33, .rather than increasing the pressurematerially at any particularradius from the axis of the drum 15. It willbe readily apparent that by this arrangement,- the adjustment disc 3| can be formed of relatively thin-and resilient material, and similarly the friction disc 33 may be relatively thin and resilient so as to readily be deformed by operation of the adjustment screw l2 toconform, in varying degrees in accordance with the actuationof the adjustment screw 12, to the dished contour. of the end 19 of the drum Hi. In this way it is possible to obtain a con siderable wide range of adjustment of the dampening effect on the drum l5 without actually deforming thedished end I9 of the drum to any material extent asthere is no positive movement of the periphery of the-drum to the left as is accomplished Whenthe holes 32 and cooperating cams 3i!v are employed as have been set forth at a radius from the drum substantially comparable to the radi-usof the drum itself. It will be readily apparent, however, that where it is desirable to be able to obtain maximum dampening, .thiscanbe obtained by the combined use of both circlesof adjustment holes 32 and32a, and cooperating cams 30 and 30a as has been described and as is illustrated in the drawing, all in accordance with the requirements of practioe.

Having. thus described a. specific embodiment of the present invention as applied to'the con struction of a particular. sash balance, it is to be understood that this form has been illustrated more particularly for disclosing the mode of operation .and the principles involved than for limitingthe present l-invention to the specific structure-.that has ..been;dis'closed, and 'it is to be un derstood'that various modifications, adaptations and. alterations can be applied to' the specific form shown to be met by the requirements of practice within the scopeof the .present invention, .except as .limited by the appended claims.

What.I claimis:

1. A sash balance comprising .in combination, a base plate havingseveral cams formed therein spaced circumferentially about a center point, a hub having one end secured to said base plate atsaid center point, an adjustment disc journaled on: said. hub having registration openings formed therein in cooperation with'said cams so asto vary-the spacingbetweeni said base plate and said. adjustment disc'iniaccordance with the relative-degree of rotation of said disc, a

drum journaled on. saidlfhub, saiddrum having a closed end'faci'ngin.the.direction of said adjustment-disc, saidclosed end being dished inwardly, a torsional spring within said drum having one end secured .to said hub and the other end secured to the inner periphery of said drum, a friction disc disposed on said hub between said drum and said adjustment disc, means bearing against the inner turns of said spring for biasing said drum against said friction disc and in the direction of said adjustment disc and said base plate.

2. A sash balancecomprising in combination, a base-plate and an adjustment disc, said .base plate and adjustment disc having cooperating registration holes and cams circumferentially located about 'a common center point so that the rotation of the adjustment disc with respect to the base plate-governs the lateral spacing of the adjustment disc from the base plataa drum, a hub secured at one .end to said base plate at said center point journaling said drum and said adjustment disc, means for biasing said drum in. the direction of said base plate and said adjustment disc upon assembly, of the balanceso as to dampen the rotation of said'drum by reason of friction applied to theside of the drum, and manually adjustable means governing the rotation of said adjustment disc relative .to said base plate whereby the extent of dampening of the rotation of said drum canbe increased subsequent to assembly of the balance.

3. A sash'balance comprising in combination, a drum, a base plate and an adjustment disc, said base plate'and adjustment disc having cooperating registration holes and cams circumferentially locatedabout a common center point ata radial distance substantially less than the radius of said drum, whereby the rotation of the adjustment disc with respect to the base plate governs the lateral spacing between the adjustment disc and the base plate, a hub secured at one end to said base plate at said center point journaling said drum and said adjustment disc, means effective upon the assembly of the sash balance for biasing said drum in the direction of said adjustment disc and thereby dampening the drum with respect to rotation by friction against the side thereof, and manually adjustable means governing the rotation of said disc relative to said base plate whereby the extent of dampening of the rotation of said drum can be increased subsequent to the assembly of the balance.

4. A'sash balance comprising, a drum having an end portion dished inwardly and providing a bearing along the'axisof the drum, a base'piate and an adjustment disc, said base plate and adjustment disc having cooperating registration holes. and-cams circumferentially located about at commonticenter point at 'a radial distance substantiallyiless than'the radius'of said drum,- a friction disc,'a hub secured at one end to said base plate atsaid center-point journaling'said drum, said friction disc and'said'adjustment disc, means effective upon assembly'of the balance for applyingpressure'at'said bearing of said drum urging said end portion of said drum against said friction disc so as to dampen the rotation of the drum, and manually adjustable means governing the rotation of said adjustment disc relative tosaidbase plate so as to adjustably increase the point, a hub having one of its ends secured to said base plate at said center point, a drum journaled on said hub, an involute spring within said drum and about said hub, said spring having its inner end secured to said hub and its outer end secured at the inner periphery of said drum, a rotatable variable pressure disc journaled on said hub between said drum and said base plate, said disc having openings disposed to register with said cams when said pressure disc is in a particular rotated position with respect to said base plate, a friction disc disposed between said pressure disc and said drum, and means bearing against the inner turns of said spring biasing said spring, said drum, said friction disc and variable pressure disc in the direction of said base plate.

6. A sash balance comprising in combination, a drum, a base plate, an adjustment disc, said base plate and adjustment disc having several cooperating registration cams formed therein at two difierent radial distances from a common axis, said cams being substantially evenly spaced about said axis, whereby the rotation of said adjustment disc relative to said base plate governs,

the lateral spacing between the adjustment disc and the base plate, a hub secured at one end to said base plate along said common axis, said hub journaling said adjustment disc and said drum, biasing means effective upon the assembly of the sash balance for biasing said drum in the direction of said adjustment disc and thereby dampening the rotation of said drum, and manually operable means governing the rotation of said adjustment disc relative to said base plate whereby the dampening of the rotation of said drum can be adjusted subsequent to the assembly of the sash balance.

7. A sash balance comprising in combination, a drum, a base plate, a friction disc, and an adjustment disc, said base plate and adjustment disc having several cooperating registration cams formed therein at a radial distance about a common axis substantially less than the radius of said drum, said cams being substantially evenly spaced circumferentially, a hub extending along said common axis secured at one end to said base plate, said hub journaling respectively said adjustment disc, said friction disc, and said drum; means effective upon the assembly of the balance to bias said drum, said friction disc, said adjustment disc and said base plate in lateral relationship respectively; and manually operable means effective subsequent to the assembly of the sash balance for rotating said adjustment disc relative to said base plate and thereby increase the dampening of the rotation of said drum by increasing the lateral spacing between said base plate and said adjustment disc.

8. A sash balance comprising, a drum, a base plate, a friction disc, an adjustment disc, said base plate and said adjustment disc having substantially evenly spaced cooperating registration cams disposed circumferentially about a common axis at a radial distance less than the radius of said drum, a hub extending along said common axis and secured at one end to said base plate, said hub journaling respectively said adjustment disc, said friction disc and said drum laterally with respect to each other; biasing means urging said drum, said friction disc, said adjustment disc and said base plate in respective lateral engagement; a face plate secured to said base plate at one end thereof, said face plate having an opening formed therein; an adjustment screw and nut, said screw being fixed with respect to axial movement and having its head accessible to a hand tool inserted through said opening in said face plate; and means for operably connecting said adjustment disc to said nut so that the axial movement of said nut along said screw effects rotation of said adjustment disc about said hub.

9. A sash balance comprising, a drum, a base plate, an involute spring, said drum having an end plate dished inwardly with a bushing loosely fitted therein and extending along the axis of said drum, a hub secured at one end to said base plate, said hub being effective to journal said bushing of said drum, an involute spring within said drum having its inner end secured to said hub and its outer end secured to the inner periphery of said drum, and biasing means acting through the inner turns of said spring urging said spring laterally against said bushing, whereby said 'bushing may be prevented from rotating with said drum by reason of said biasin means, while said drum is free to rotate on said bushing.

10, A sash balance comprising in combination, a base plate having several cams formed therein and spaced cireumferentially about a center point, a hub secured at one end to said base plate at said center point, an adjustment disc journaled on said hub having registration openings formed therein in cooperation with said cams so as to permit said adjustment disc to be in direct lateral contact with said base plate when in a particular rotated position with respect to said base plate, but to be laterally spaced from said base plate to a variable extent as said adjustment disc is rctated, a drum journaled on said hub, a friction disc between said drum and said hub, and biasing means eifective upon the assembly of the balance for biasing said drum against said friction disc.

11. A sash balance comprising, a base plate, a hub secured to said base plate, a drum rotatable on said hub, an involute spring Within said drum having its inner end secured to said hub and its outer end secured to said drum to rotate therewith, a ring shaped bearing element on said hub within said drum, said drum having an end wall with an opening therein adapted to journal on said hub, and arcuate sectors formed inwardly from said wall leaving radial spokes therebetwen, such sectors having the arcuate surfaces concentric with said opening and of suitable diameter to form a radial bearing when associated with the outer periphery of said ring shaped bearing element, means for biasing the inner coils of said involute spring against the ring shaped bearing element and the Wall of said drum, and flexible suspension means coilable on the outer periphery of said drum and having one end secured to the drum and the opposite end attachable to a window sash, whereby said drum is rotated on movement of said window sash and force to balance said window sash is stored in the involute spring on downward movement of said window sash.

DEWITT TAPPAN.

REFERENCES CITEB The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 488,699 Rosentreter et a1. Dec. 27, 1892 522,624 Smith July 10, 1894 2,241,969 Tappan May 13, 1941 2,534,968 Haas Dec. 19, 1950 

